1. Field of the Invention
The present invention relates to a fluid measuring device capable of measuring fluid characteristics such as the type and velocity of various fluids easily and accurately even when it is difficult to allow an ultrasonic signal to pass through the fluid in a pipeline.
2. Background of the Related Art
Gas pipeline for supplying town gas and pipelines such as water or sewage pipelines are buried under the ground. When construction works are performed in a place where pipelines are buried, these pipelines may be exposed and it may be difficult to identify the type of the exposed pipeline. In such a case, it is necessary to determine the type of the exposed pipeline by determining the type of fluid flowing through the pipeline (for example, the type of fluid such as town gas, water, or air) and to take measures appropriate for each type of pipeline.
As a conventional method of determining the type of fluid in a pipeline, a method of forming a hole in a pipeline and extracting the fluid through the hole is known. According to another method of determining the type of fluid in a pipeline, a neutron moisture meter is used. This method can determine the fluid type without breaking a pipeline. As still another method of determining the type of fluid in a pipeline, Japanese Patent Application Publication No. H11-94613 (Patent Literature 1) discloses a method of determining the fluid type based on transmission intensity of ultrasonic waves. Moreover, Japanese Patent No. 4687293 (Patent Literature 2) discloses a method of measuring a flow rate distribution of liquid in a pipeline by allowing ultrasonic waves to pass through the pipeline without breaking the pipeline.
However, the method of determining the type of a fluid in a pipeline by extracting internal fluid through a hole requires a pipeline recovery operation of blocking the hole after the type of fluid in the pipeline is determined, which incurs a considerable time and labor.
Moreover, the method of determining the type of fluid in the pipeline using a neutron moisture meter can identify the presence of water only. Thus, the type of fluid that can be identified is limited, and it is difficult to determine a sufficient number of types of fluid.
Further, the method of determining the type of fluid in the pipeline using the transmission intensity of ultrasonic waves, disclosed in Patent Literature 1 requires an ultrasonic probe to be provided in a pipeline, and as a result, a complex piping work is required.
Moreover, when the method disclosed in Patent Literature 2 is applied to gas such as town gas or air, since the transmittance of ultrasonic waves in gas is lower than that in liquid, it is difficult to obtain sufficient measurement accuracy. Further, when a pipeline is old, rusty, or corroded, or has sediments adhering thereto, which makes it difficult for ultrasonic waves to pass through, sufficiently accurate measurement is difficult to implement.
The present invention has been made in view of the above problems, and an object thereof is to provide a fluid measuring device capable of measuring fluid characteristics such as the type and velocity of various fluids easily and accurately even when it is difficult to allow an ultrasonic signal to pass through the fluid in a pipeline.